In recent years, measurement of colors has become more and more important and color data such as spectral reflection coefficients and color measurement of various samples have been used at places of production in many fields such as painting, printing, textile, ceramics, agriculture, forestry and fishery industries. Particularly, in the food industry and the like, products are evaluated and/or are subjected to pass/fail tests with reference to particular or unique index or indices originally defined by a user and calculated using, as variables, color measurement values measured and calculated in accordance with a general-purpose calorimetric system such as an XYZ colorimetric system, an L*a*b* colorimetric system, or an L*C*h° calorimetric system.
The index or indices are often originally defined for each object to be evaluated, such as for coffee, tomatoes, beers, orange or juices, or are defined differently with the entities, units or organizations of the evaluators, such as among the countries, districts, industries or companies. Thus, it is almost impossible to store all these index or indices in a controller of a calorimeter beforehand.
Accordingly, in the case when colors of various samples, to be measured need to be expressed by user-defined index or indices, a manufacturer of colorimeters was requested to manufacture custom-model colorimeters with an additional calculating function for the user-defined index or indices. Or color measurement values according to a general-purpose calorimetric system were obtained by an external computing unit such as a personal computer from a colorimeter, in which the color measurement values are converted into the user-defined index or indices. However, in the case of manufacturing of the custom model, there exists a problem with many costs and longer time for remodeling of a generally used model. In the case of using the external computing unit, there is a problem that a special computing program must be prepared for converting the color measurement values into the user-defined indices. Further, in the latter case, since both the colorimeter and the external computing unit are always required for the measurement, there are additional problems that they are inferior in portability and convenience of handling.